Ionization recording capsules



Feb. 17, 1959 w. H. BARKAS 2,374,299

' IONIZATION RECORDING CAPSULES Filed June 30. 1952 Hrotographic emulsion Go/ot/he Protective coating Photograph/c emulsion Protective coating INVENT R. Walter hf arkos- Unite States Patent TONIZATIQN RECDRDING CAPSULES Walter H. Barkers, Oakland, Calif.

Application June 35, 1952, Serial No. 296,532

Claims. (Ci. 250-65) (Granted under Title35, U. S. Code (1952), sec. 266) The invention described herein may be manufactured and used by and for the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

This invention relates to a means for measuring the integrated intensity of ionizing radiations traversing a small region and, more particularly, to an ionization recording capsule.

Prior art devices for ionization measurements have ineluded Geiger counters, scintillation counters, crystal conductivity counters, ionization chambers, cloud chambers and photographic emulsions.

Counters and ionization chambers are cumbersome and require Wires leading to them and none have .beenmade small enough for satisfactory use in small animals. In addition, it is difiicult to match the counter to the composition of the organic medium in which it is to be immersed. Cloud chambers are entirely unsuitable for measurements in a small region. Radiation monitors using X-ray film have been developed for external use but no combination of suitable emulsion mounting for the emulsion and container is known which makes possible the measurement of the true ionization at any point in a small test animal.

An object, therefore, of the present invention is to provide an instrument for such measurement of small diluensions and of which the composition very nearly matches that of its environment so that the presence of the instrument does not alter the ionization observed in a living organism from that which would exist in the absence of the detector.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Fig. 1 illustrates a greatly enlarged cross-section of an ionization capsule embodying the present invention; and

Fig. 2 illustrates another embodiment of the capsule of the invention made with tubing.

Reference is made to the drawing wherein numeral 1 indicates a volume of photographic emulsion which may be as small as 0.001 cubic millimeter encased in a protective coat 2 of photographic gelatin of the order of perhaps 25 microns in thickness. This coating of gelatin prevents mechanical damage to the emulsion which might render some grains of the silver bromide developable. It also provides a strong tough mounting for the emulsion and matches the composition of an organic environment. Gelatin is particularly suitable for this purpose also because it permits diffusion through it of the developing, fixing and washing solutions required in processing the emulsion and, furthermore, gelatin has no deleterious chemical reaction-on the emulsion which might render grains of the emulsion developable.

The gelatin-coated pellet of emulsion is finally encased in envelope 3 of opaque material which is sealed against entry of fluids from the organism to the emulsion and should be preferably an organic material that approximatelvmatches the composition of the environment in Which It is to be placed but can, as required, be a metal or some other composition of matter. In most cases the requirements for the envelope will be met by using,

rubber of the type employed in surgery, which is known to have no irritating effect on living tissue. Rubber closely matches fat in composition andthe presence of such a capsule, especially since it is very small, cannot much change the radiation density traversing the point where it is placed from that which would have existed in its ab sence.

The manufacture of such capsules can be carried out by coating small fragments of emulsion with gelatin and, after drying, inserting them into small pieces of cured rubber and sealing the openings. .More specifically, fine rubber tubing can be cut into short lengths, the pellet of gelatinemulsion inserted and the ends sealed shut by heat or cement. To open, the sealed ends can be sliced off as with a microtome and the pellets pushed out. Thus the external diameter of the envelope need notexceed one millimeter.

In Fig. 2 is shown a capsule made with tubing but with the gelatine omitted, as is quite permissible. The emulsion 4, as a liquid, is forced into the fine tubing 5 of rubber-like material. The tubing is then cut ch in short pieces and the ends 6 are sealed shut either by heat or wth rubber cement or the like. The final pellet, with the emulsion solidified, is used in manner similar tothepellet of Fig. 1. if desired, a microtome can be used to slice out a thin, typical cross-section of the pellet which, after development, is then used as the ionization-measuring sample element.

When the pellet is to be used in a dry environment with no moisture that would penetrate the gelatine it is possible to omit the rubber-like impervious outer coating. In such a case the emulsion-gelatine pellet is rendered opaque, if necessary, by an opaque stain applied to the outside of the gelatine.

To measure the radiation received by the emulsion, capsules from the same batch of emulsion should be divided into three groups which receive an identical development. Group (a) should be exposed to no radiation except cosmic rays. Group (12) should receive a known amount of radiation from a standard source such as radium. Group (0) consists of those capsules used to measure unknown radiation dosages. Each pellet is studied microscopically, and in equal volumes of emulsion, the number of developed grains and tracks of ionizing particles tabulated.

The radiation received at the test position can then be by secondary processes; they produce charged particles v in their interaction with matter and these charged particles produce ionization. The ionizing radiations produce developable grains in photographic emulsions. Emulsions now available are capable of producing a track of developable grains when any high speed charged particle traverses a few microns of the emulsion, and it is these that are preferred for use with this invention.

The observed grain density and rate of change of grain density along the track are sufiicient to determine both the nature and energy of the particle which produced the track. Thus, in principle, an absolute assessment of the energy expended in the emulsion by ionizing radiations is possible without the use of a radiation standard. However, for most purposes the simpler procedure of merely comparing the grain densityor blackening of the emulsion with that produced by a standard source of radiation will provide as much information as needed. Under such a procedure ordinary emulsions will serve and highly specialized or exceedingly sensitive emulsions will not be required as a general rule. Care must always be exercised, however, to avoid exposure of the emulsion to low energy, non-penetrating radiation such as light which also is capable of producing developable grains.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

l. An article of manufacture for measuring ionization radiation in a particular environment, comprising a pellet containing photographic emulsion, a coating of gelatin covering said pellet, and on outer optically opaque covering surrounding said coated pellet, said opaque covering being of substantially the same density as, and being composed of substantially the same chemical elements in substantially the same proportions as the material of said environment.

2. An article of maufacture for measuring ionizing radiations comprising a pellet containing a photographic emulsion and an optically opaque covering surrounding said pellet, said opaque covering being of elastomer.

3. An article of manufacture for measuring ionizing radiations in a particular environment, comprising a pellet containing a photographic emulsion, a coating covering said pellet of material adapted to protect said pellet from mechanical damage and being pervious to developing solutions, said coating material being of such composition as not chemically to react with the grains of the emulsion to render them developable, and substantially matching in radiation characteristics said environment, and an outer optically opaque covering surrounding said coated pellet, said opaque covering being of substantially the same density as, and being composed of substantially the same chemical elements in susbtantially the same proportions as the material of said environment.

4. An article of manufacture comprising a pellet containing photographic emulsion and an optically opaque covering enveloping said pellet.

5. The article of claim 4 wherein said emulsion is of the type capable of producing a track of developable grains when any high speed charged particle traverses a few microns thereof. 4

References Cited in the file of this patent UNITED STATES PATENTS 2,469,204

Peters May 3, 1949 2,565,378 Land Aug. 21, 1951 2,584,029 Land Jan. 29, 1952 2,600,064 McCune June 10, 1952 OTHER REFERENCES 

1. AN ARTICLE OF MANUFACTURE FOR MEASURING IONIZATION RADIATION IN A PARTICULAR ENVIROMENT, COMPRISING A PELLET CONTAINING PHOTOGRAPHIC EMULSION, A COATING OF GELATIN COVERING SAID PELLET, AND ON OUTER OPTICALLY OPAQUE COVERING SUROUNDING SAID COATED PELLET, SAID OPAQUE COVERING BEING OF SUBSTANTIALLY THE SAME DENSITY AS, AND BEING COMPOSED OF SUBSTANTIALLY THE SAME CHEMICAL ELEMENTS IN SUBSTANTIALLY ATHE SAME PORPORTIONS AS THE MATERIAL OF SAID ENVIROMENT. 